Instinctively I try to avoid giving our 1 year old sugar. However, I don't really understand why it is bad for her.

Often when she doesn't want to eat any more savoury food she is more than happy to have something sweet - fruit or yoghurt or sometimes even (I blame her mother!) a bit of cake. At this age she has not been influenced by advertising or other social factors and is acting out of instinct - some form of evolutionary impulse which has aided human development for a very long time. This leads me to think that maybe sugar may have some benefits for infants and is actually quite important for them to have some.

I realise there is a difference between natural fruit sugars and highly refined sugar. Also in ancient times sugar was no way nearly as available as it is today.

What research has been carried out on the effects of sugar, and the effects of different forms of sugar on infants? How harmful / beneficial is it? It there a recommended daily amount?

3 Answers
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Short version:Once a child is older than 6 months, small amounts of sugar (sugar in moderation) are probably okay, but refined sugars should be avoided, and fruit juice intake should be restricted and monitored (The American Academy of Pediatrics (AAP) recommends limiting juice intake to 4-6 ounces (118-177 milliliters) for kids under 7 years old, and no more than 8-12 ounces (237-355 milliliters) of juice for older kids and teens.). Too many sweets can lead to obesity, tooth decay, and continuing patterns of increased sugar and fat consumption in later life.

Sugar is a form of simple carbohydrate. Consuming simple carbohydrates allows the blood sugar level to rise very quickly. Naturally occurring simple sugars aren't necessarily bad, as they often include a number of other nutritionally useful components, such as vitamins. Refined sugars lack nutritional value, yet are more likely to be eaten in greater quantities because they taste great, and aren't too filling. Worse, they tend to be high in calories, potentially leading to obesity issues.

This study investigated the impact of early sugar introduction on long-term sugar consumption patterns, among other factors.

At 12 and 24 mo, total sugar intake was correlated with total fat intake (both p≥.001) even when adjusted for weight. Total sugar intake at 12 and 24 mo was correlated with lean mass(p=.9 and p=.06). Additionally, 24 mo sugar intake/kg was positively correlated with total sugar intake/kg at 12 mo, p≥.001. Unlike adult data that shows a calorie compensation effect (an inverse relationship between consumption of calories from sugar and fat) the 12 and 24 mo data show positive correlations between high sugar and high fat intake. In addition, there was no correlation between sugar intake and lean mass at 12 or 24 mo. High sugar intake/kg at 12 mo is positively correlated with high sugar intake/kg at 24 mo suggesting a developing pattern of sweet preference. Infants developing a sweet preference may “pattern” their eating habits for later in the toddler years for sugar and fat intake.

So higher consumption of sugar in infants can result in higher consumption of fat, and may establish a pattern of a preference for sweet and fatty foods that could persist into later years.

There is no nutritional indication to feed juice to infants younger than 6 months. Offering juice before solid foods are introduced into the diet could risk having juice replace breast milk or infant formula in the diet. This can result in reduced intake of protein, fat, vitamins, and minerals such as iron, calcium, and zinc.37 Malnutrition and short stature in children have been associated with excessive consumption of juice.4,38

and

Teeth begin to erupt at approximately 6 months of age. Dental caries have also been associated with juice consumption.39 Prolonged exposure of the teeth to the sugars in juice is a major contributing factor to dental caries

For toddlers and young children:

Fruit juice and fruit drinks are easily overconsumed by toddlers and young children because they taste good. In addition, they are conveniently packaged or can be placed in a bottle and carried around during the day. Because juice is viewed as nutritious, limits on consumption are not usually set by parents. Like soda, it can contribute to energy imbalance. High intakes of juice can contribute to diarrhea, overnutrition or undernutrition, and development of dental caries.

Dental issues are a recurring theme in professional concern about consumption of sugar by infants (presumably not an issue prior to the teeth actually erupting, but teeth generally start to erupt around 6 months of age, and prior to six months infants should only be consuming breastmilk and/or formula). The American Dental Association warns against sugary liquids, or using sugar on pacifiers:

Another factor for tooth decay is the frequent, prolonged exposure of the baby’s teeth to liquids that contain sugar, like sweetened water and fruit juice and potentially milk, breast milk and formula. Tooth decay can occur when the baby is put to bed with a bottle, or when a bottle is used as a pacifier for a fussy baby. The sugary liquids pool around the teeth while the child sleeps. Bacteria in the mouth use these sugars as food. They then produce acids that attack the teeth. Each time your child drinks these liquids, acids attack for 20 minutes or longer. After multiple attacks, the teeth can decay.

Pacifiers dipped in sugar or honey can also lead to tooth decay since the sugar or honey can provide food for the bacteria’s acid attacks.

+1 for all the great links. Especially the links to the studies.
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Meg CoatesFeb 21 '12 at 15:57

I don't have a direct reference to any studies but apparently in either Mindless Eating or her book about overeating Ellyn Satter (an RD) talks about how sugar can override the body's built-in food intake regulation and cause the body to take in more calories than it needs.
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justktJul 30 '13 at 20:30

Evolutionary conditioning for sweet tooth

Evolutionarily, indeed sweet foods have offered an advantage to their consumers: lots of calories. Almost all of us - not just infants, but most adults, in fact, most animals too - are attracted by sweet flavours because of this. But especially us humans, since our big brains crave a lot of energy. And even more so for children, who require an immense amount of energy for their growth, and the tremendous amount of physical and mental (learning) activity they perform daily. It is so much easier to get one's needed energy intake from e.g. honey or fruits than from raw vegetables or meat, much less from grass.

As you note, for a long long time sugar was not available in its pure form, the closest to that used to be honey (or maybe maple syrup in some locations). It was a rare treat, not an everyday indulgence, thus in nature there was no risk of overeating it. Nowadays there is, but we don't have a built-in protection against it. It is now widely known that it can cause tooth decay, also obesity, and subsequently heart disease and other illnesses, but there may be other issues too.

Nutritional value (or lack thereof)

I am not a medical expert, so this is only my subjective take about the issue. In its raw form, be it in honey, cane or fruits, there are lots of other useful stuff - vitamins, minerals etc. - in the food apart from sugar. These provide nutritional value, and help absorbing and digesting sugar. I have read that digesting sugar actually requires vitamin B2, which normally is present in the honey / fruit, but not in refined sugar. So not only is refined sugar absent of any nutritional value, but consuming it in fact depletes your vitamin resources further. So it is advisable to limit sugar intake, and replace refined sugar with (fresh or dried) fruits, raw cane / demerara sugar etc.

Blood sugar level and mental / energy state

There are also lots of different kinds of sugars and sugarlike materials (e.g. starch). Some are absorbed faster, some slower. When sugar is digested, it gets into the blood, raising blood sugar level. In natural food, sugar is absorbed slower since its concentration is lower, it is surrounded by lots of other nutrients and it may also need to be transformed first into another form of sugar (glucose) which is directly usable for our body. Thus blood sugar level rises gently, and since digestion takes longer, it is sustained fairly steadily for a longer period of time. Higher blood sugar levels make you active, energetic and positive. When the sugar level starts to decline, you get hungry again - and also tired, and potentially angry or in a bad mood - and the cycle repeats. Refined sugar, however, is absorbed much faster, so it kicks up blood sugar levels faster and to higher levels, potentially making one overly agitated. Soon after that, blood sugar level drops, since there is no steady supply, potentially causing a sharp mood swing towards fatigue and depression. That's when a lot of us reach for the next candy bar, to revive and repeat the cycle...

Hypoglycemia and diabetes

My wife has a condition commonly called hypoglycemia. She is very sensitive to variations in her blood sugar level, thus absolutely can't fast, and must get regular meals in about every 3 hours, otherwise she turns into a dragon. She had suffered from an almost manic-depressive intensity of the ups and downs described above, for many years, before she somehow happened to realize it was caused by sugar. Since then, she more or less successfully restricts her intake of refined sugar (fruit sugar is OK), keeping her mood swings at bay.

According to the book Sugar Blues, hypoglycemia is actually pretty common, just most people never actually realise it is caused by refined sugar. The book also claims that it can turn into diabetes proper if left unnoticed for years or decades. I think the book contains some pretty extreme opinions which I don't identify with (like linking sugar with bubonic plague), however I think there is at least a grain of truth in many of its statements. E.g. as per my wife's story, I can see how in some extreme cases sugar may cause symptoms (mis)diagnosed as a mental illness. Also, its explanation of how prolonged repetition of the above high-low blood sugar cycle may eventually wear out the pancreas so much that it stops producing insulin, resulting in (type 1) diabetes, sounds plausible to me. I would be very interested to hear scientific opinion about these claims.

Effects on children

Children are typically more sensitive to such effects, and in my personal experience, refined sugar intake can have dramatic effects on them. On our own (and others') children, we have regularly observed hyperactivity and sometimes very difficult behaviour after taking lots of sweets (in birthday parties etc.), then intense fatigue or hysteric breakdown after an hour or two. So we try to reduce their sugar intake towards the socially acceptable minimum (without being overzealous). IIRC they got almost no refined sugar below 1y, and still not much after that (except at birthday parties etc.) until they started to eat the same food as us adults.

This is only our own subjective experience though, and AFAIK there are no scientific studies to prove this effect (or at least, the scientists conducting such studies may have been singles without children :-).

This is a potentially great answer, but you really need to cite sources. Per our faq: "Please note that opinions shared here should be backed up either with a reference, or experiences that happened to you personally."
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BeofettFeb 21 '12 at 14:10

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@Beofett, thanks for the fedback. I added a reference.
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Péter TörökFeb 21 '12 at 15:00

Thanks! I'd still like to see a reference for the B2 being depleted by refined sugar (I'd never heard that before), but +1 from me for the rest.
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BeofettFeb 21 '12 at 15:23

@Beofett, oops, I missed that. It is also from Sugar Blues.
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Péter TörökFeb 21 '12 at 15:28

Sugar is "quick energy" for lack of a better term. If the body is given a choice of energy-producing molecules (fat, protein, or sugar), it will take the sugar first because it requires very little effort for the body to breakdown polysaccharides or disaccharides into the simple sugars needed to push through cellular respiration and generate energy. Fat and protein require a few extra steps and are, thus, more work. Likewise, our brain works 100% off glucose (commonly called blood sugar) which is the body's favorite type of monosaccharide.

Dr. Sears claims that babies are born with a certain affinity for sugar, and I've read similar statements in other places. This sort of makes sense. Breastmilk, from what I understand, has a bit of a sweet taste to it--probably to help encourage nursing. Obviously, infants who nursed better had a greater likelihood of survival than those who didn't, and mothers of these infants had more children survive into adulthood probably simply because they had more children survive in general.

I don't (personally) think that there's anything wrong with giving your daughter fruit or yogurt after she's eaten her dinner or lunch. Fructose is a perfectly natural sugar, as is lactose, though you have to watch out with yogurt since many manufacturers will add more sugar to their yogurt so always check your labels (some yogurt recipes call for a small amount of sugar to feed the bacterial cultures, but I am certain that yogurt manufacturers are using sugar in excess of what is needed). Additionally, when your daughter eats these foods, she's receiving other nutrients from the dairy or fruit she's eating (potassium from bananas, proteins from dairy, etc.).

We all, know, though that there is little nutritional value in cake or candy. I think (again, personally) it's just a bad habit to start giving kids too much by way of refined sugars too early. In moderation, as a treat every so often, it's ok, but giving it too much sets your kid up for poor eating habits, and in some circles it's even thought that sugar can be addicting. However, if you institute the "no refined sugar" rule, then you risk your kid going crazy with it whenever she is put in a situation when you aren't there to supervise (think slumber parties when she's older, school, etc.).

The American Heart Association came out with a daily refined sugar intake recommendation. They recommend no more than 20 g of sugar (5 tsp) for adult women per day, 36 g (9 tsp) for adult men, and 12 g (3 tsp) for children. The article doesn't break down the children's amount into specific ages, but I would imagine anything below that would be acceptable for babies/very young children. However, the AHA stresses that natural sugars (complex carbs like those found in whole grains, sugars from whole fruits, dairy sugars) do not need to be avoided.